odb/source-loose.c

#include "git-compat-util.h"
#include "abspath.h"
#include "chdir-notify.h"
#include "gettext.h"
#include "hex.h"
#include "loose.h"
#include "object-file.h"
#include "object-file-convert.h"
#include "odb.h"
#include "odb/source-files.h"
#include "odb/source-loose.h"
#include "odb/streaming.h"
#include "oidtree.h"
#include "path.h"
#include "repository.h"
#include "strbuf.h"
#include "tempfile.h"
#include "write-or-die.h"

static int append_loose_object(const struct object_id *oid,
			       const char *path UNUSED,
			       void *data)
{
	oidtree_insert(data, oid, NULL);
	return 0;
}

static struct oidtree *odb_source_loose_cache(struct odb_source_loose *loose,
					      const struct object_id *oid)
{
	int subdir_nr = oid->hash[0];
	struct strbuf buf = STRBUF_INIT;
	size_t word_bits = bitsizeof(loose->subdir_seen[0]);
	size_t word_index = subdir_nr / word_bits;
	size_t mask = (size_t)1u << (subdir_nr % word_bits);
	uint32_t *bitmap;

	if (subdir_nr < 0 ||
	    (size_t) subdir_nr >= bitsizeof(loose->subdir_seen))
		BUG("subdir_nr out of range");

	bitmap = &loose->subdir_seen[word_index];
	if (*bitmap & mask)
		return loose->cache;
	if (!loose->cache) {
		ALLOC_ARRAY(loose->cache, 1);
		oidtree_init(loose->cache);
	}
	strbuf_addstr(&buf, loose->base.path);
	for_each_file_in_obj_subdir(subdir_nr, &buf,
				    loose->base.odb->repo->hash_algo,
				    append_loose_object,
				    NULL, NULL,
				    loose->cache);
	*bitmap |= mask;
	strbuf_release(&buf);
	return loose->cache;
}

static int quick_has_loose(struct odb_source_loose *loose,
			   const struct object_id *oid)
{
	return !!oidtree_contains(odb_source_loose_cache(loose, oid), oid);
}

static int read_object_info_from_path(struct odb_source_loose *loose,
				      const char *path,
				      const struct object_id *oid,
				      struct object_info *oi,
				      enum object_info_flags flags)
{
	int ret;
	int fd;
	unsigned long mapsize;
	void *map = NULL;
	git_zstream stream, *stream_to_end = NULL;
	char hdr[MAX_HEADER_LEN];
	size_t size_scratch;
	enum object_type type_scratch;
	struct stat st;

	/*
	 * If we don't care about type or size, then we don't
	 * need to look inside the object at all. Note that we
	 * do not optimize out the stat call, even if the
	 * caller doesn't care about the disk-size, since our
	 * return value implicitly indicates whether the
	 * object even exists.
	 */
	if (!oi || (!oi->typep && !oi->sizep && !oi->contentp)) {
		struct stat st;

		if ((!oi || (!oi->disk_sizep && !oi->mtimep)) && (flags & OBJECT_INFO_QUICK)) {
			ret = quick_has_loose(loose, oid) ? 0 : -1;
			goto out;
		}

		if (lstat(path, &st) < 0) {
			ret = -1;
			goto out;
		}

		if (oi) {
			if (oi->disk_sizep)
				*oi->disk_sizep = st.st_size;
			if (oi->mtimep)
				*oi->mtimep = st.st_mtime;
		}

		ret = 0;
		goto out;
	}

	fd = git_open(path);
	if (fd < 0) {
		if (errno != ENOENT)
			error_errno(_("unable to open loose object %s"), oid_to_hex(oid));
		ret = -1;
		goto out;
	}

	if (fstat(fd, &st)) {
		close(fd);
		ret = -1;
		goto out;
	}

	mapsize = xsize_t(st.st_size);
	if (!mapsize) {
		close(fd);
		ret = error(_("object file %s is empty"), path);
		goto out;
	}

	map = xmmap(NULL, mapsize, PROT_READ, MAP_PRIVATE, fd, 0);
	close(fd);
	if (!map) {
		ret = -1;
		goto out;
	}

	if (oi->disk_sizep)
		*oi->disk_sizep = mapsize;
	if (oi->mtimep)
		*oi->mtimep = st.st_mtime;

	stream_to_end = &stream;

	switch (unpack_loose_header(&stream, map, mapsize, hdr, sizeof(hdr))) {
	case ULHR_OK:
		if (!oi->sizep)
			oi->sizep = &size_scratch;
		if (!oi->typep)
			oi->typep = &type_scratch;

		if (parse_loose_header(hdr, oi) < 0) {
			ret = error(_("unable to parse %s header"), oid_to_hex(oid));
			goto corrupt;
		}

		if (*oi->typep < 0)
			die(_("invalid object type"));

		if (oi->contentp) {
			*oi->contentp = unpack_loose_rest(&stream, hdr, *oi->sizep, oid);
			if (!*oi->contentp) {
				ret = -1;
				goto corrupt;
			}
		}

		break;
	case ULHR_BAD:
		ret = error(_("unable to unpack %s header"),
			    oid_to_hex(oid));
		goto corrupt;
	case ULHR_TOO_LONG:
		ret = error(_("header for %s too long, exceeds %d bytes"),
			    oid_to_hex(oid), MAX_HEADER_LEN);
		goto corrupt;
	}

	ret = 0;

corrupt:
	if (ret && (flags & OBJECT_INFO_DIE_IF_CORRUPT))
		die(_("loose object %s (stored in %s) is corrupt"),
		    oid_to_hex(oid), path);

out:
	if (stream_to_end)
		git_inflate_end(stream_to_end);
	if (map)
		munmap(map, mapsize);
	if (oi) {
		if (oi->sizep == &size_scratch)
			oi->sizep = NULL;
		if (oi->typep == &type_scratch)
			oi->typep = NULL;
		if (oi->delta_base_oid)
			oidclr(oi->delta_base_oid, loose->base.odb->repo->hash_algo);
		if (oi->source_infop && !ret)
			oi->source_infop->source = &loose->base;
	}

	return ret;
}

static int odb_source_loose_read_object_info(struct odb_source *source,
					     const struct object_id *oid,
					     struct object_info *oi,
					     enum object_info_flags flags)
{
	struct odb_source_loose *loose = odb_source_loose_downcast(source);
	static struct strbuf buf = STRBUF_INIT;

	/*
	 * The second read shouldn't cause new loose objects to show up, unless
	 * there was a race condition with a secondary process. We don't care
	 * about this case though, so we simply skip reading loose objects a
	 * second time.
	 */
	if (flags & OBJECT_INFO_SECOND_READ)
		return -1;

	odb_loose_path(loose, &buf, oid);
	return read_object_info_from_path(loose, buf.buf, oid, oi, flags);
}

/*
 * Find "oid" as a loose object in given source, open the object and return its
 * file descriptor. Returns the file descriptor on success, negative on failure.
 *
 * The "path" out-parameter will give the path of the object we found (if any).
 * Note that it may point to static storage and is only valid until another
 * call to open_loose_object().
 */
static int open_loose_object(struct odb_source_loose *loose,
			     const struct object_id *oid, const char **path)
{
	static struct strbuf buf = STRBUF_INIT;
	int fd;

	*path = odb_loose_path(loose, &buf, oid);
	fd = git_open(*path);
	if (fd >= 0)
		return fd;

	return -1;
}

static void *odb_source_loose_map_object(struct odb_source_loose *loose,
					 const struct object_id *oid,
					 unsigned long *size)
{
	const char *p;
	int fd = open_loose_object(loose, oid, &p);
	void *map = NULL;
	struct stat st;

	if (fd < 0)
		return NULL;

	if (!fstat(fd, &st)) {
		*size = xsize_t(st.st_size);
		if (!*size) {
			/* mmap() is forbidden on empty files */
			error(_("object file %s is empty"), p);
			goto out;
		}

		map = xmmap(NULL, *size, PROT_READ, MAP_PRIVATE, fd, 0);
	}

out:
	close(fd);
	return map;
}

struct odb_loose_read_stream {
	struct odb_read_stream base;
	git_zstream z;
	enum {
		ODB_LOOSE_READ_STREAM_INUSE,
		ODB_LOOSE_READ_STREAM_DONE,
		ODB_LOOSE_READ_STREAM_ERROR,
	} z_state;
	void *mapped;
	unsigned long mapsize;
	char hdr[32];
	int hdr_avail;
	int hdr_used;
};

static ssize_t read_istream_loose(struct odb_read_stream *_st, char *buf, size_t sz)
{
	struct odb_loose_read_stream *st =
		container_of(_st, struct odb_loose_read_stream, base);
	size_t total_read = 0;

	switch (st->z_state) {
	case ODB_LOOSE_READ_STREAM_DONE:
		return 0;
	case ODB_LOOSE_READ_STREAM_ERROR:
		return -1;
	default:
		break;
	}

	if (st->hdr_used < st->hdr_avail) {
		size_t to_copy = st->hdr_avail - st->hdr_used;
		if (sz < to_copy)
			to_copy = sz;
		memcpy(buf, st->hdr + st->hdr_used, to_copy);
		st->hdr_used += to_copy;
		total_read += to_copy;
	}

	while (total_read < sz) {
		int status;

		st->z.next_out = (unsigned char *)buf + total_read;
		st->z.avail_out = sz - total_read;
		status = git_inflate(&st->z, Z_FINISH);

		total_read = st->z.next_out - (unsigned char *)buf;

		if (status == Z_STREAM_END) {
			git_inflate_end(&st->z);
			st->z_state = ODB_LOOSE_READ_STREAM_DONE;
			break;
		}
		if (status != Z_OK && (status != Z_BUF_ERROR || total_read < sz)) {
			git_inflate_end(&st->z);
			st->z_state = ODB_LOOSE_READ_STREAM_ERROR;
			return -1;
		}
	}
	return total_read;
}

static int close_istream_loose(struct odb_read_stream *_st)
{
	struct odb_loose_read_stream *st =
		container_of(_st, struct odb_loose_read_stream, base);

	if (st->z_state == ODB_LOOSE_READ_STREAM_INUSE)
		git_inflate_end(&st->z);
	munmap(st->mapped, st->mapsize);
	return 0;
}

static int odb_source_loose_read_object_stream(struct odb_read_stream **out,
					       struct odb_source *source,
					       const struct object_id *oid)
{
	struct odb_source_loose *loose = odb_source_loose_downcast(source);
	struct object_info oi = OBJECT_INFO_INIT;
	struct odb_loose_read_stream *st;
	unsigned long mapsize;
	void *mapped;

	mapped = odb_source_loose_map_object(loose, oid, &mapsize);
	if (!mapped)
		return -1;

	/*
	 * Note: we must allocate this structure early even though we may still
	 * fail. This is because we need to initialize the zlib stream, and it
	 * is not possible to copy the stream around after the fact because it
	 * has self-referencing pointers.
	 */
	CALLOC_ARRAY(st, 1);

	switch (unpack_loose_header(&st->z, mapped, mapsize, st->hdr,
				    sizeof(st->hdr))) {
	case ULHR_OK:
		break;
	case ULHR_BAD:
	case ULHR_TOO_LONG:
		goto error;
	}

	oi.sizep = &st->base.size;
	oi.typep = &st->base.type;

	if (parse_loose_header(st->hdr, &oi) < 0 || st->base.type < 0)
		goto error;

	st->mapped = mapped;
	st->mapsize = mapsize;
	st->hdr_used = strlen(st->hdr) + 1;
	st->hdr_avail = st->z.total_out;
	st->z_state = ODB_LOOSE_READ_STREAM_INUSE;
	st->base.close = close_istream_loose;
	st->base.read = read_istream_loose;

	*out = &st->base;

	return 0;
error:
	git_inflate_end(&st->z);
	munmap(mapped, mapsize);
	free(st);
	return -1;
}

struct for_each_object_wrapper_data {
	struct odb_source_loose *loose;
	const struct object_info *request;
	odb_for_each_object_cb cb;
	void *cb_data;
};

static int for_each_object_wrapper_cb(const struct object_id *oid,
				      const char *path,
				      void *cb_data)
{
	struct for_each_object_wrapper_data *data = cb_data;

	if (data->request) {
		struct object_info oi = *data->request;

		if (read_object_info_from_path(data->loose, path, oid, &oi, 0) < 0)
			return -1;

		return data->cb(oid, &oi, data->cb_data);
	} else {
		return data->cb(oid, NULL, data->cb_data);
	}
}

static int for_each_prefixed_object_wrapper_cb(const struct object_id *oid,
					       void *node_data UNUSED,
					       void *cb_data)
{
	struct for_each_object_wrapper_data *data = cb_data;
	if (data->request) {
		struct object_info oi = *data->request;

		if (odb_source_read_object_info(&data->loose->base,
						oid, &oi, 0) < 0)
			return -1;

		return data->cb(oid, &oi, data->cb_data);
	} else {
		return data->cb(oid, NULL, data->cb_data);
	}
}

static int odb_source_loose_for_each_object(struct odb_source *source,
					    const struct object_info *request,
					    odb_for_each_object_cb cb,
					    void *cb_data,
					    const struct odb_for_each_object_options *opts)
{
	struct odb_source_loose *loose = odb_source_loose_downcast(source);
	struct for_each_object_wrapper_data data = {
		.loose = loose,
		.request = request,
		.cb = cb,
		.cb_data = cb_data,
	};

	/* There are no loose promisor objects, so we can return immediately. */
	if ((opts->flags & ODB_FOR_EACH_OBJECT_PROMISOR_ONLY))
		return 0;
	if ((opts->flags & ODB_FOR_EACH_OBJECT_LOCAL_ONLY) && !source->local)
		return 0;

	if (opts->prefix)
		return oidtree_each(odb_source_loose_cache(loose, opts->prefix),
				    opts->prefix, opts->prefix_hex_len,
				    for_each_prefixed_object_wrapper_cb, &data);

	return for_each_loose_file_in_source(source, for_each_object_wrapper_cb,
					     NULL, NULL, &data);
}

struct find_abbrev_len_data {
	const struct object_id *oid;
	unsigned len;
};

static int find_abbrev_len_cb(const struct object_id *oid,
			      struct object_info *oi UNUSED,
			      void *cb_data)
{
	struct find_abbrev_len_data *data = cb_data;
	unsigned len = oid_common_prefix_hexlen(oid, data->oid);
	if (len != hash_algos[oid->algo].hexsz && len >= data->len)
		data->len = len + 1;
	return 0;
}

static int odb_source_loose_find_abbrev_len(struct odb_source *source,
					    const struct object_id *oid,
					    unsigned min_len,
					    unsigned *out)
{
	struct odb_source_loose *loose = odb_source_loose_downcast(source);
	struct odb_for_each_object_options opts = {
		.prefix = oid,
		.prefix_hex_len = min_len,
	};
	struct find_abbrev_len_data data = {
		.oid = oid,
		.len = min_len,
	};
	int ret;

	ret = odb_source_for_each_object(&loose->base, NULL, find_abbrev_len_cb,
					 &data, &opts);
	*out = data.len;

	return ret;
}

static int count_loose_object(const struct object_id *oid UNUSED,
			      struct object_info *oi UNUSED,
			      void *payload)
{
	unsigned long *count = payload;
	(*count)++;
	return 0;
}

static int odb_source_loose_count_objects(struct odb_source *source,
					  enum odb_count_objects_flags flags,
					  unsigned long *out)
{
	struct odb_source_loose *loose = odb_source_loose_downcast(source);
	const unsigned hexsz = source->odb->repo->hash_algo->hexsz - 2;
	char *path = NULL;
	DIR *dir = NULL;
	int ret;

	if (flags & ODB_COUNT_OBJECTS_APPROXIMATE) {
		unsigned long count = 0;
		struct dirent *ent;

		path = xstrfmt("%s/17", source->path);

		dir = opendir(path);
		if (!dir) {
			if (errno == ENOENT) {
				*out = 0;
				ret = 0;
				goto out;
			}

			ret = error_errno("cannot open object shard '%s'", path);
			goto out;
		}

		while ((ent = readdir(dir)) != NULL) {
			if (strspn(ent->d_name, "0123456789abcdef") != hexsz ||
			    ent->d_name[hexsz] != '\0')
				continue;
			count++;
		}

		*out = count * 256;
		ret = 0;
	} else {
		struct odb_for_each_object_options opts = { 0 };
		*out = 0;
		ret = odb_source_for_each_object(&loose->base, NULL, count_loose_object,
						 out, &opts);
	}

out:
	if (dir)
		closedir(dir);
	free(path);
	return ret;
}

static int odb_source_loose_freshen_object(struct odb_source *source,
					   const struct object_id *oid,
					   const time_t *mtime)
{
	struct odb_source_loose *loose = odb_source_loose_downcast(source);
	static struct strbuf path = STRBUF_INIT;
	odb_loose_path(loose, &path, oid);
	return !!check_and_freshen_file(path.buf, 1, mtime);
}

/* Finalize a file on disk, and close it. */
static void close_loose_object(struct odb_source_loose *loose,
			       int fd, const char *filename)
{
	if (loose->base.will_destroy)
		goto out;

	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
		odb_transaction_files_fsync(loose->base.odb->transaction, fd, filename);
	else if (fsync_object_files > 0)
		fsync_or_die(fd, filename);
	else
		fsync_component_or_die(FSYNC_COMPONENT_LOOSE_OBJECT, fd,
				       filename);

out:
	if (close(fd) != 0)
		die_errno(_("error when closing loose object file"));
}

/* Size of directory component, including the ending '/' */
static inline int directory_size(const char *filename)
{
	const char *s = strrchr(filename, '/');
	if (!s)
		return 0;
	return s - filename + 1;
}

/*
 * This creates a temporary file in the same directory as the final
 * 'filename'
 *
 * We want to avoid cross-directory filename renames, because those
 * can have problems on various filesystems (FAT, NFS, Coda).
 */
static int create_tmpfile(struct repository *repo,
			  struct strbuf *tmp, const char *filename)
{
	int fd, dirlen = directory_size(filename);

	strbuf_reset(tmp);
	strbuf_add(tmp, filename, dirlen);
	strbuf_addstr(tmp, "tmp_obj_XXXXXX");
	fd = git_mkstemp_mode(tmp->buf, 0444);
	if (fd < 0 && dirlen && errno == ENOENT) {
		/*
		 * Make sure the directory exists; note that the contents
		 * of the buffer are undefined after mkstemp returns an
		 * error, so we have to rewrite the whole buffer from
		 * scratch.
		 */
		strbuf_reset(tmp);
		strbuf_add(tmp, filename, dirlen - 1);
		if (mkdir(tmp->buf, 0777) && errno != EEXIST)
			return -1;
		if (adjust_shared_perm(repo, tmp->buf))
			return -1;

		/* Try again */
		strbuf_addstr(tmp, "/tmp_obj_XXXXXX");
		fd = git_mkstemp_mode(tmp->buf, 0444);
	}
	return fd;
}

/**
 * Common steps for loose object writers to start writing loose
 * objects:
 *
 * - Create tmpfile for the loose object.
 * - Setup zlib stream for compression.
 * - Start to feed header to zlib stream.
 *
 * Returns a "fd", which should later be provided to
 * end_loose_object_common().
 */
static int start_loose_object_common(struct odb_source_loose *loose,
				     struct strbuf *tmp_file,
				     const char *filename, unsigned flags,
				     git_zstream *stream,
				     unsigned char *buf, size_t buflen,
				     struct git_hash_ctx *c, struct git_hash_ctx *compat_c,
				     char *hdr, int hdrlen)
{
	const struct git_hash_algo *algo = loose->base.odb->repo->hash_algo;
	const struct git_hash_algo *compat = loose->base.odb->repo->compat_hash_algo;
	int fd;
	struct repo_config_values *cfg = repo_config_values(loose->base.odb->repo);

	fd = create_tmpfile(loose->base.odb->repo, tmp_file, filename);
	if (fd < 0) {
		if (flags & ODB_WRITE_OBJECT_SILENT)
			return -1;
		else if (errno == EACCES)
			return error(_("insufficient permission for adding "
				       "an object to repository database %s"),
				     loose->base.path);
		else
			return error_errno(
				_("unable to create temporary file"));
	}

	/*  Setup zlib stream for compression */
	git_deflate_init(stream, cfg->zlib_compression_level);
	stream->next_out = buf;
	stream->avail_out = buflen;
	git_hash_init(c, algo);
	if (compat && compat_c)
		git_hash_init(compat_c, compat);

	/*  Start to feed header to zlib stream */
	stream->next_in = (unsigned char *)hdr;
	stream->avail_in = hdrlen;
	while (git_deflate(stream, 0) == Z_OK)
		; /* nothing */
	git_hash_update(c, hdr, hdrlen);
	if (compat && compat_c)
		git_hash_update(compat_c, hdr, hdrlen);

	return fd;
}

/**
 * Common steps for the inner git_deflate() loop for writing loose
 * objects. Returns what git_deflate() returns.
 */
static int write_loose_object_common(struct odb_source_loose *loose,
				     struct git_hash_ctx *c, struct git_hash_ctx *compat_c,
				     git_zstream *stream, const int flush,
				     unsigned char *in0, const int fd,
				     unsigned char *compressed,
				     const size_t compressed_len)
{
	const struct git_hash_algo *compat = loose->base.odb->repo->compat_hash_algo;
	int ret;

	ret = git_deflate(stream, flush ? Z_FINISH : 0);
	git_hash_update(c, in0, stream->next_in - in0);
	if (compat && compat_c)
		git_hash_update(compat_c, in0, stream->next_in - in0);
	if (write_in_full(fd, compressed, stream->next_out - compressed) < 0)
		die_errno(_("unable to write loose object file"));
	stream->next_out = compressed;
	stream->avail_out = compressed_len;

	return ret;
}

/**
 * Common steps for loose object writers to end writing loose objects:
 *
 * - End the compression of zlib stream.
 * - Get the calculated oid to "oid".
 */
static int end_loose_object_common(struct odb_source_loose *loose,
				   struct git_hash_ctx *c, struct git_hash_ctx *compat_c,
				   git_zstream *stream, struct object_id *oid,
				   struct object_id *compat_oid)
{
	const struct git_hash_algo *compat = loose->base.odb->repo->compat_hash_algo;
	int ret;

	ret = git_deflate_end_gently(stream);
	if (ret != Z_OK)
		return ret;
	git_hash_final_oid(oid, c);
	if (compat && compat_c)
		git_hash_final_oid(compat_oid, compat_c);

	return Z_OK;
}

static int write_loose_object(struct odb_source_loose *loose,
			      const struct object_id *oid, char *hdr,
			      int hdrlen, const void *buf, unsigned long len,
			      const time_t *mtime, unsigned flags)
{
	int fd, ret;
	unsigned char compressed[4096];
	git_zstream stream;
	struct git_hash_ctx c;
	struct object_id parano_oid;
	static struct strbuf tmp_file = STRBUF_INIT;
	static struct strbuf filename = STRBUF_INIT;

	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
		odb_transaction_files_prepare(loose->base.odb->transaction);

	odb_loose_path(loose, &filename, oid);

	fd = start_loose_object_common(loose, &tmp_file, filename.buf, flags,
				       &stream, compressed, sizeof(compressed),
				       &c, NULL, hdr, hdrlen);
	if (fd < 0)
		return -1;

	/* Then the data itself.. */
	stream.next_in = (void *)buf;
	stream.avail_in = len;
	do {
		unsigned char *in0 = stream.next_in;

		ret = write_loose_object_common(loose, &c, NULL, &stream, 1, in0, fd,
						compressed, sizeof(compressed));
	} while (ret == Z_OK);

	if (ret != Z_STREAM_END)
		die(_("unable to deflate new object %s (%d)"), oid_to_hex(oid),
		    ret);
	ret = end_loose_object_common(loose, &c, NULL, &stream, &parano_oid, NULL);
	if (ret != Z_OK)
		die(_("deflateEnd on object %s failed (%d)"), oid_to_hex(oid),
		    ret);
	if (!oideq(oid, &parano_oid))
		die(_("confused by unstable object source data for %s"),
		    oid_to_hex(oid));

	close_loose_object(loose, fd, tmp_file.buf);

	if (mtime) {
		struct utimbuf utb = {
			.actime = *mtime,
			.modtime = *mtime,
		};

		if (utime(tmp_file.buf, &utb) < 0 &&
		    !(flags & ODB_WRITE_OBJECT_SILENT))
			warning_errno(_("failed utime() on %s"), tmp_file.buf);
	}

	return finalize_object_file_flags(loose->base.odb->repo, tmp_file.buf, filename.buf,
					  FOF_SKIP_COLLISION_CHECK);
}

static int odb_source_loose_write_object(struct odb_source *source,
					 const void *buf, size_t len,
					 enum object_type type,
					 const struct object_id *oid,
					 const struct object_id *compat_oid,
					 const time_t *mtime,
					 enum odb_write_object_flags flags)
{
	struct odb_source_loose *loose = odb_source_loose_downcast(source);
	char hdr[MAX_HEADER_LEN];
	int hdrlen;

	hdrlen = format_object_header(hdr, sizeof(hdr), type, len);

	if (write_loose_object(loose, oid, hdr, hdrlen, buf, len, mtime, flags))
		return -1;

	if (compat_oid)
		return repo_add_loose_object_map(loose, oid, compat_oid);

	return 0;
}

static int odb_source_loose_write_object_stream(struct odb_source *source,
						struct odb_write_stream *in_stream,
						size_t len,
						struct object_id *oid)
{
	struct odb_source_loose *loose = odb_source_loose_downcast(source);
	const struct git_hash_algo *compat = loose->base.odb->repo->compat_hash_algo;
	struct object_id compat_oid;
	int fd, ret, err = 0, flush = 0;
	unsigned char compressed[4096];
	git_zstream stream;
	struct git_hash_ctx c, compat_c;
	struct strbuf tmp_file = STRBUF_INIT;
	struct strbuf filename = STRBUF_INIT;
	unsigned char buf[8192];
	int dirlen;
	char hdr[MAX_HEADER_LEN];
	int hdrlen;

	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
		odb_transaction_files_prepare(loose->base.odb->transaction);

	/* Since oid is not determined, save tmp file to odb path. */
	strbuf_addf(&filename, "%s/", loose->base.path);
	hdrlen = format_object_header(hdr, sizeof(hdr), OBJ_BLOB, len);

	/*
	 * Common steps for write_loose_object and stream_loose_object to
	 * start writing loose objects:
	 *
	 *  - Create tmpfile for the loose object.
	 *  - Setup zlib stream for compression.
	 *  - Start to feed header to zlib stream.
	 */
	fd = start_loose_object_common(loose, &tmp_file, filename.buf, 0,
				       &stream, compressed, sizeof(compressed),
				       &c, &compat_c, hdr, hdrlen);
	if (fd < 0) {
		err = -1;
		goto cleanup;
	}

	/* Then the data itself.. */
	do {
		unsigned char *in0 = stream.next_in;

		if (!stream.avail_in && !in_stream->is_finished) {
			ssize_t read_len = odb_write_stream_read(in_stream, buf,
								 sizeof(buf));
			if (read_len < 0) {
				close(fd);
				err = -1;
				goto cleanup;
			}

			stream.avail_in = read_len;
			stream.next_in = buf;
			in0 = buf;
			/* All data has been read. */
			if (in_stream->is_finished)
				flush = 1;
		}
		ret = write_loose_object_common(loose, &c, &compat_c, &stream, flush, in0, fd,
						compressed, sizeof(compressed));
		/*
		 * Unlike write_loose_object(), we do not have the entire
		 * buffer. If we get Z_BUF_ERROR due to too few input bytes,
		 * then we'll replenish them in the next input_stream->read()
		 * call when we loop.
		 */
	} while (ret == Z_OK || ret == Z_BUF_ERROR);

	if (stream.total_in != len + hdrlen)
		die(_("write stream object %"PRIuMAX" != %"PRIuMAX), (uintmax_t)stream.total_in,
		    (uintmax_t)len + hdrlen);

	/*
	 * Common steps for write_loose_object and stream_loose_object to
	 * end writing loose object:
	 *
	 *  - End the compression of zlib stream.
	 *  - Get the calculated oid.
	 */
	if (ret != Z_STREAM_END)
		die(_("unable to stream deflate new object (%d)"), ret);
	ret = end_loose_object_common(loose, &c, &compat_c, &stream, oid, &compat_oid);
	if (ret != Z_OK)
		die(_("deflateEnd on stream object failed (%d)"), ret);
	close_loose_object(loose, fd, tmp_file.buf);

	if (odb_freshen_object(loose->base.odb, oid)) {
		unlink_or_warn(tmp_file.buf);
		goto cleanup;
	}
	odb_loose_path(loose, &filename, oid);

	/* We finally know the object path, and create the missing dir. */
	dirlen = directory_size(filename.buf);
	if (dirlen) {
		struct strbuf dir = STRBUF_INIT;
		strbuf_add(&dir, filename.buf, dirlen);

		if (safe_create_dir_in_gitdir(loose->base.odb->repo, dir.buf) &&
		    errno != EEXIST) {
			err = error_errno(_("unable to create directory %s"), dir.buf);
			strbuf_release(&dir);
			goto cleanup;
		}
		strbuf_release(&dir);
	}

	err = finalize_object_file_flags(loose->base.odb->repo, tmp_file.buf, filename.buf,
					 FOF_SKIP_COLLISION_CHECK);
	if (!err && compat)
		err = repo_add_loose_object_map(loose, oid, &compat_oid);
cleanup:
	strbuf_release(&tmp_file);
	strbuf_release(&filename);
	return err;
}

static int odb_source_loose_begin_transaction(struct odb_source *source UNUSED,
					      struct odb_transaction **out UNUSED,
					      enum odb_transaction_flags flags UNUSED)
{
	/* TODO: this is a known omission that we'll want to address eventually. */
	return error("loose source does not support transactions");
}

static int odb_source_loose_read_alternates(struct odb_source *source UNUSED,
					    struct strvec *out UNUSED)
{
	return 0;
}

static int odb_source_loose_write_alternate(struct odb_source *source UNUSED,
					    const char *alternate UNUSED)
{
	return error("loose source does not support alternates");
}

static void odb_source_loose_clear_cache(struct odb_source_loose *loose)
{
	oidtree_clear(loose->cache);
	FREE_AND_NULL(loose->cache);
	memset(&loose->subdir_seen, 0,
	       sizeof(loose->subdir_seen));
}

static void odb_source_loose_prepare(struct odb_source *source,
				     enum odb_prepare_flags flags)
{
	struct odb_source_loose *loose = odb_source_loose_downcast(source);
	if (flags & ODB_PREPARE_FLUSH_CACHES)
		odb_source_loose_clear_cache(loose);
}

static void odb_source_loose_close(struct odb_source *source UNUSED)
{
	/* Nothing to do. */
}

static void odb_source_loose_reparent(const char *name UNUSED,
				      const char *old_cwd,
				      const char *new_cwd,
				      void *cb_data)
{
	struct odb_source_loose *loose = cb_data;
	char *path = reparent_relative_path(old_cwd, new_cwd,
					    loose->base.path);
	free(loose->base.path);
	loose->base.path = path;
}

static void odb_source_loose_free(struct odb_source *source)
{
	struct odb_source_loose *loose = odb_source_loose_downcast(source);
	odb_source_loose_clear_cache(loose);
	loose_object_map_clear(&loose->map);
	chdir_notify_unregister(NULL, odb_source_loose_reparent, loose);
	odb_source_release(&loose->base);
	free(loose);
}

struct odb_source_loose *odb_source_loose_new(struct object_database *odb,
					      const char *path,
					      bool local)
{
	struct odb_source_loose *loose;

	CALLOC_ARRAY(loose, 1);
	odb_source_init(&loose->base, odb, ODB_SOURCE_LOOSE, path, local);

	loose->base.free = odb_source_loose_free;
	loose->base.close = odb_source_loose_close;
	loose->base.prepare = odb_source_loose_prepare;
	loose->base.read_object_info = odb_source_loose_read_object_info;
	loose->base.read_object_stream = odb_source_loose_read_object_stream;
	loose->base.for_each_object = odb_source_loose_for_each_object;
	loose->base.find_abbrev_len = odb_source_loose_find_abbrev_len;
	loose->base.count_objects = odb_source_loose_count_objects;
	loose->base.freshen_object = odb_source_loose_freshen_object;
	loose->base.write_object = odb_source_loose_write_object;
	loose->base.write_object_stream = odb_source_loose_write_object_stream;
	loose->base.begin_transaction = odb_source_loose_begin_transaction;
	loose->base.read_alternates = odb_source_loose_read_alternates;
	loose->base.write_alternate = odb_source_loose_write_alternate;

	if (!is_absolute_path(loose->base.path))
		chdir_notify_register(NULL, odb_source_loose_reparent, loose);

	return loose;
}